A Serious Question (reposed from D300 forum)

I found an ultra-compact P&S to be extremely convenient on trips. Something like a Canon SD series or equivalent. I always had it in my pocket on many trips and got moments I wouldn't get otherwise. These also have a usable movie mode, and I'm sure your kids would love to see their parents enjoy themselves somewhere.
Don't baby this thing, either.

For when you have the space to carry I'd seriously look into some of the micro-4/3 cameras that are coming out. While inferior to a DSLR they're also smaller. They seem to be miles ahead of a P&S in terms of image quality and responsiveness.

The 200-400 isn't a general walk around lens, you'll have to get some shorter lenses too, for more weight, cost, and worry.

If you opt for a DSLR I wouldn't get much more than a D300+18-200vr for travel, honestly.

The $100k figure is a bit misleading, since it works out to $6.5k per trip. That's a fancy trip, but not priced out of the ordinary. A large camera purchase can blow the budget on that. A D3x amortized over 4 trips is still $2k